When you look at the big picture, it's not surprising. In short, we don’t have enough fresh water, and things are getting worse.

Four billion people already face severe water scarcity at least one month each year, according to a recent study. Supply will tighten as populations grow and demand rises for not only drinking water but also use in manufacturing, electricity, and more. At the same time, the world faces rising temperatures and many areas will suffer declining precipitation.

Water is already a luxury in some places. GDP per capita and water consumption are clearly linked in the Middle East.

Many countries are dealing with multiple water-related hotspots. Cambodia, for instance, is flood-prone, cyclone-prone, drought-prone, and unusually exposed to climate change, with poor access to drinking water and poor-access to sanitation.

Another major problem is water quality, which is projected to deteriorate significantly due to chemical pollutants. The map below shows how much water quality risk will increase by 2050.

America’s problems with water quality are tied to infrastructure decline. Without more investment, the country faces more incidents like the recent discovery of lead-poisoning in Michigan.

Bill Pugliano/Getty Images

Control of water resources will be a growing source of tension worldwide. For instance, countries may fight for access to five great river systems in the equatorial region known as the Great World Desert.

Take the Nile: "There appears to be an inevitable collision between Egypt’s need for water, as a downstream user, and rising needs upstream to satisfy growing populations in Sudan and Ethiopia," writes Professor James Lee in "Climate Change and Armed Conflict."

Also worrying: eight of the ten longest rivers in Asia originate in China in some way, with six coming from Tibet. "China’s ability to control these waters and use them internally will be a central geopolitical issue," writes Lee.

Tensions could also rise over cloud seeding to generate rain, even though this technique does not actually steal rain from neighboring areas. "Countries have gone to war over less," Lee said in Esquire.

An agricultural aircraft flies over Nakhonsawan province, in a bid to seed clouds, north of Bangkok, Thailand July 9, 2015.REUTERS/Chaiwat Subprasom